Conventionally, a production method using a sodium silicate solution, which is referred to as water glass, as a starting material is known as a method for producing a silica sol (Patent Literature 1). In the production method, the sodium silicate solution is treated once with a cation exchange resin to remove ions such as sodium ion. Thus, purity as a starting material is increased, and then the resultant is used for producing a silica sol.
However, in a production method of Patent Literature 1, high purification of a starting material by ion exchange has limitations.
Then, as a method for obtaining a high purity silica sol, methods including using hydrolysis of a high purity alkoxysilane such as ethyl orthosilicate are disclosed (Patent Literatures 2 to 4).
Patent Literatures 2 to 4 disclose a 2 liquid reaction type method for producing a silica sol including addition of a liquid containing an alkoxysilane and an organic solvent to a liquid containing an alkaline catalyst, water, and an organic solvent. The 2 liquid reaction type method for producing a silica sol cannot increase a concentration of each material in a reaction solution, and thus it is hard to produce a silica sol at a high concentration, which leads to problems in productivity.
With respect to the above-mentioned problems, Patent Literature 5 discloses a 3 liquid reaction type method for producing a silica sol including addition of an organic solvent containing tetramethoxysilane and a solvent containing an alkaline catalyst and water to an organic solvent containing an alkaline catalyst and water. According to such a method, it may be possible to highly concentrate silica particles in a reaction solution.